Dehydration of gases with liquid desiccants

ABSTRACT

A gas drying method is disclosed in which gas streams are dehydrated to low dew points by contacting the wet gas with a dry liquid desiccant, with the liquid desiccant regenerated by heating it in a reboiler containing an internal reboiler vapor condenser and stripping it with a stripping agent that is dried with solid desiccant.

This application is a continuation in part of Ser. No. 08/409,867, filedMar. 24, 1995 now U.S. Pat. No. 5,643,421.

FIELD OF THE INVENTION

This invention relates to the separation and removal of water from agas-water mixture using a liquid desiccant, as well as the removal ofwater from the liquid desiccant such that the liquid desiccant can bereused. The dehydration of gas is accomplished with a relatively lowoperating cost and without creating a toxic vapor disposal systemconcern.

DESCRIPTION OF THE RELATED ART

Natural gas, refinery gas, carbon dioxide, hydrogen, synthesis gas, gasfrom an oil production facility and other industrial gases are oftenused in circumstances that require the water in these gases to beremoved. Water may be removed, for example, to prevent the formation ofhydrates in downstream processes and pipelines, meet dew pointspecifications for the sale of the gas, and to prevent corrosionassociated with wet gas.

There are two general categories of gas dehydration systems; soliddesiccant and liquid desiccant. Liquid desiccant systems are relativelysimple to operate and easy to maintain. Unfortunately, the liquiddesiccant systems are typically unable to produce treated gases withextremely low levels of moisture. Solid desiccant systems are often usedto provide gas with very low levels of moisture, however these plantscan be more complex and expensive to operate than liquid desiccantsystems. They also present a higher risk of downstream damage by failureof automatic regeneration switching valves. Thus, there is a continuingneed for a relatively simple liquid desiccant gas dehydration systemthat produces gas with the low moisture content normally associated withsolid desiccant systems.

Hygroscopic liquids such as triethylene glycol, diethylene glycol andtetraethylene glycol are commonly used liquid desiccants. In the typicalliquid desiccant system, a substantially dry glycol, such as one of thethose listed above, is introduced to the top of a contactor. The liquiddesiccant flows downward through the contactor while at the same time,wet gas is introduced at the bottom of the contactor. When the liquiddesiccant and gas contact each other, the liquid desiccant absorbs waterfrom the gas. Water-rich liquid desiccant is removed from the bottom ofthe contactor, while dry gas leaves the top of the contactor. Waterabsorbed by the liquid desiccant is removed by the application of heatand the liquid desiccant is regenerated and reused. The dryness of thegas, expressed as its dew point depends on several factors, includingthe water content of the dry liquid desiccant, the number of theoreticalstages in the contactor and the liquid desiccant and gas flow rates. Thedew point of the dry gas leaving the contactor decreases as the watercontent of the dry liquid desiccant decreases. To produce a dry gas witha very low dew point, it is essential that the dry liquid desiccantentering the contactor have an extremely low moisture content.

The regeneration of spent liquid desiccant is typically accomplished byheating it in order to vaporize the water it has absorbed from the wetgas. The concentration of water in a regenerated liquid desiccantdepends in part on the regeneration temperature and pressure.Theoretically, it is possible to produce liquid desiccant with very lowlevels of water by subjecting the liquid desiccant to high temperatures.However, as the regeneration temperature approaches the boiling point ofpure liquid desiccant, the liquid desiccant thermally decomposes. Toavoid this problem, the thermal regeneration of liquid desiccants isusually limited to temperatures below the thermal decomposition point ofthe liquid desiccant. This results in a relatively high concentration ofwater in the regenerated liquid desiccant. The higher concentration ofwater in the liquid desiccant produces gas from the contactor with ahigher than desirable dew point. To date, attempts to deal with theproblem of producing very low dew point gas with a liquid desiccantsystem have met with limited success.

In one process, described in U. S. Pat. No. 3,105,748, an aliquot ofdried natural gas is heated to 325 F. to 365F. in a gas-fired heater.The gas is passed through glycol maintained at the same temperature.This gas strips water from the glycol and produces a regenerated glycolwith a lower concentration of water than can be obtained with heat aloneat the indicated regeneration temperature. The stripping gas is theneither vented or flared. This practice, however, has the undesirableeffects of wasting gas and polluting the atmosphere. Moreover, the hotglycol may also contain toxic components such as benzene and toluene,absorbed from the gas that is dried in the process. When stripping gasis applied to the wet glycol, these toxic components are purged in amanner that does not permit their condensation at ambient conditions.While it is possible to compress the stripping gas in order to reuse thegas and facilitate the condensation of its toxic components, this is ahigh maintenance and high cost solution.

In another process, described in U. S. Pat. No. 3,349,544, anazeotroping agent is introduced below the surface of the liquiddesiccant in a regeneration zone. The regeneration zone is maintained ata temperature above the vaporization temperature of the azeotropingagent. The vaporized azeotroping mixture is condensed and the water isremoved from the azeotrope. The azeotroping agent is then recycled. Theazeotroping agent acts as a moisture carrier, allowing the regenerationzone to be operated at a lower partial pressure of water vapor. Thisproduces drier liquid desiccant without subjecting the liquid desiccantto excessively high regeneration temperatures. While this azeotropingagent process produces a regenerated liquid desiccant with a lowermoisture content than can be achieved in a conventional liquid desiccantprocess, the moisture content of the liquid desiccant cannot be reducedbelow the equilibrium concentration dictated by the partial pressure ofwater in the regeneration zone.

In an improvement over the process described in U. S. Pat. No.3,349,544, presented in U. S. Pat. No. 4,005,997, the recoveredazeotroping agent is vaporized, superheated to the regenerationtemperature and fed to an isothermal stripper in counter current contactwith semi-lean hot liquid desiccant produced from the liquid desiccantregenerator. The additional stripping action at the regenerationtemperature improves the performance of the azeotroping agent, removingmore water than the process described in U. S. Pat. No. 3,349,544.Again, the azeotroping agent is no more than a moisture carrier thatfurther improves the regeneration with additional stripping action. Theminimum moisture content of the liquid desiccant cannot be reduced belowthe equilibrium water content dictated by the operating temperature andpressure.

In another patent, U.S. Pat. No. 4,332,643, wet glycol desiccant is fedto a still having a reboiler. The wet glycol desiccant is concentratedand recovered from the still as a reboiler liquid. The reboiler liquidis then conveyed to a water exhauster for removal of much of theremaining water. The water exhauster is partially filled with reboilerliquid which is in equilibrium with the vapor in the vapor space abovethat liquid. That equilibrium is disturbed by condensing vapor in thevapor space of the exhauster, trapping and removing this condensate. Theliquid within the exhauster will then attempt to reattain equilibrium byfurther vaporization. Under vapor-liquid equilibrium conditions, thevapor is substantially more rich in water than the liquid with which itis in equilibrium. In time, the water content of the liquid phase willapproach exhaustion so that the residual liquid will approach 100%glycol concentration. The liquid in the exhauster, which consequentlyhas a very low moisture content, is used to contact wet gas in acontactor. The condensed liquid removed from the water exhauster ismixed with the wet glycol feed to the still. This process is able toachieve an enhancement of the glycol purity without the use of a primarystripping gas medium, as is found in U.S. Pat. No. 3,349,544.

SUMMARY OF THE INVENTION

This invention is directed to an improved liquid desiccant dehydrationof gases wherein the regeneration of wet liquid desiccant to very lowlevels of moisture enables the process to produce dry gas with extremelylow dew points. This dehydration is accomplished with low operatingcosts and with little release of harmful hydrocarbons that are oftenfound in natural gas streams. The invention accomplishes this bystripping partially dehydrated liquid desiccant with a dried strippingagent or solvent and condensing and removing a portion of the vaporgenerated by the heater that heats the wet liquid desiccant.

One aspect of the invention is to produce a liquid desiccant with a verylow moisture content. When this low moisture liquid desiccant is used todry gas, the moisture content of the dried gas is 0.1 ppm or lower, alevel suitable for cryogenic processing.

Another aspect of the invention is that it utilizes a reboiler vaporcondenser in conjunction with the reboiler, permitting substantialenergy savings. The configuration of the present invention overcomes theoperational and other difficulties of using a condenser with a reboiler,such as those associated with the invention disclosed in U.S. Pat. No.4,332,643. For example, the present invention is not prone to creating apartial vacuum in the area of the reboiler condenser. Further, unlikethe invention disclosed in U.S. Pat. No. 4,332,643, the presentinvention does not require the introduction of blanket gas into thesystem. The light gas introduction, as found in U.S. Pat. No. 4,332,643,`purges` heavy aromatic components absorbed by the liquid desiccant,creating a toxic vapor disposal concern. Instead, the present inventionutilizes a configuration wherein pressurized solvent is vaporized andadded to the regeneration system, maintaining positive pressure andthereby avoiding the possibility of partial vacuum in the reboiler.

Another aspect of the invention concerns reducing the moisture contentof the solvent used as a stripping agent during the regeneration of theliquid desiccant such that the regenerated liquid desiccant has amoisture content of 10 ppm and lower. This is accomplished by drying thesolvent in a solid-liquid contactor containing a commercially availablesolid desiccant such as silica gel, alumina gel, alumina or molecularsieves.

Additional features of the present invention include the recovery oflight hydrocarbons removed from the wet gas for use as solvent, and theseparation and removal of noncondensable gases and lighter componentsfrom the liquid desiccant.

The liquid desiccant of the invention is a hygroscopic liquid.Representative liquid desiccants are well known in the art and includepolyols alone or in a mixture. Typical polyols include liquid compoundssuch as ethylene glycol, propylene glycol, butylene glycol, pentyleneglycol, glycerol, trimethyol propane, diethylene glycol, triethyleneglycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol,tetrapropylene glycol, and mixtures thereof. These glycols contain from2 to 12 carbon atoms.

Polyol compounds which are normally solid, but which are substantiallysoluble in anhydrous liquid polyols or liquid hydroxyl amines, may alsobe used as liquid desiccants. Typical of these solid polyol compoundsare erythritol, sorbitol, pentaerythritol and low molecular weightsugars. Typical hydroxyl amines include alkanolamines, such asmonoethanol amine, diethanol amine, triethanol amine, iso-propanolamine, including mono, di, and tri, isopropanol amine or diglycolamine.The alkanolamines can contain from 2 to 9 carbon atoms.

A stripping agent is employed to regenerate the liquid desiccant to ahigher purity. The stripping agent also acts as a solvent that absorbshydrocarbons that were removed from the wet gas in the contactor by theliquid desiccant. The solvent can be a liquid hydrocarbon, eitheraliphatic or aromatic, or mixtures thereof, which is substantiallyinsoluble in the liquid desiccant and in water, and which has a boilingtemperature between from about 40 C. and about 160 C. A non-hydrocarboncould also be used as a solvent. The non-hydrocarbon solvent would havea boiling range of about 80 C. to about 100 C. for 90% of the mixturewith an end point not greater than about 130 C. The specific gravity ofthe non-hydrocarbon solvent would need to be between about 0.7 to about0.9 to permit economical solvent-water separation. The solvent will alsoconsist of hydrocarbons removed from the gas that is dried in thecontactor. Preferably, the solubility of the solvent in the liquiddesiccant should not exceed about 5 percent.

Liquid aliphatic hydrocarbons may include alkanes, cycloalkanes,alkenes, and cycloalkenes with normal boiling points in the range ofabout 40 C. to about 160 C. Representative aliphatic hydrocarbonsinclude the straight and branched chain monoalkenes and alkanes havingfrom 6 to 10 carbon atoms and mixtures thereof. Representative aromatichydrocarbons include benzene, toluene, xylene, ethyl benzene, and thelike. Representative mixtures of aliphatic and/or aromatic hydrocarbonsinclude petroleum fractions in the desired boiling range such as naphthaand natural gasoline, which can include in the mixture hydrocarbons withnumber of carbon atoms as low as 3, and as high as 15.

In practicing the invention, substantially dry liquid desiccant isintroduced to the top of a contacting zone and wet gas is introduced atthe bottom of the contacting zone. The liquid desiccant flows downcountercurrent to the gas flow and absorbs water from the gas. The drygas leaving the contacting zone is suitable for use in applicationsdemanding extremely low dew point gas. The wet liquid desiccant leavingthe contacting zone is regenerated for reuse in the contacting zone. Thewet liquid desiccant is initially heated and then flashed to removesubstantially all hydrocarbons in the wet desiccant, and other lowmolecular weight components, such as nitrogen, carbon dioxide, andhydrogen sulfide.

The flashed wet liquid desiccant is introduced to a first stripping zonewhere it is heated and also stripped by vaporized solvent received fromthe overhead of a second stripping zone, described below. The heat canbe provided by a conventional heat exchanger, a direct fired heater, aconventional stripper reboiler or any of the other systems well known tothose with skill in the art. The overhead of the first stripping zonecontains water, solvent, and light components. The bottoms of the firststripping zone contains partially dehydrated liquid desiccant.

The partially dehydrated liquid desiccant bottoms from the firststripping zone is introduced into a second stripping zone where itswater is stripped by dried, vaporized solvent. The overhead of thesecond stripping zone, which contains vaporized solvent and waterremoved from the partially dehydrated liquid desiccant, is fed to thefirst stripping zone, where it acts as a stripping agent.

Solvent, water and other light products from the overhead of the firststripping zone are cooled and decanted in one or more separators.Solvent is recovered form the separator and dried to a very low moisturecontent in a conventional solid-liquid contacting zone that containscommercially available solid desiccant. The solid desiccant could besilica gel, alumina gel, alumina or molecular sieves. Two desiccant bedsare typically employed. One bed would be on-stream, absorbing water fromthe solvent, while the other bed is being regenerated and cooled. Thesolid desiccant is regenerated by passing a heated gas through it. Themoist hot vapor stream exiting the regenerating bed can be cooled,condensing the water to facilitate its removal. The regeneration can beaccomplished with any hot superheated gas. Readily available gassuitable for regeneration would include dry gas leaving the contactor orvaporized solvent.

Once dried, the solvent is vaporized and used as a stripping agent inthe second stripping zone. The use of extremely dry solvent as thestripping agent in the second stripping zone produces a liquid desiccantwith a very low moisture content. When this low moisture content liquiddesiccant is used in the contacting zone, it produces dry gas with dewpoints significantly lower than can be achieved in the conventionalliquid desiccant dehydrators found in the prior art.

At least a portion of the vapor generated in the heater is in directcontact with a vapor condenser placed in the vapor space above theliquid that is not vaporized in the heater. This vapor, unlike theliquid that remains unvaporized, is rich in water. The vapor thatcondenses is removed from the vapor space, changing the equilibrium andcausing water in the liquid to vaporize. The remaining liquid, which asa result of the vapor condensing and removal process, has a greatlyreduced water content, requires a reduced amount of solvent stripping inthe second stripping zone.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a gas dehydration systemaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 represents the preferred embodiment of the present invention.Contacting zone 10 is a conventional gas-liquid contacting column. Aninlet 11 for the wet gas is located in the contacting zone below thecontacting device, (typically trays or packing). Dried gas is removedfrom outlet 13. Dry liquid desiccant enters the contacting zone 10 atinlet 15. Wet liquid desiccant enters the contacting zone 10 at inlet15. Wet liquid desiccant is removed from outlet 17.

Wet liquid desiccant flows via line 17 through internal reboiler vaporcondenser 120 where it is used as a cooling fluid wherein it isincrementally heated by about 5 C. to about 20 C. The wet liquiddesiccant leaves reboiler vapor condenser 120 via line 121 and is usedas the fluid for cooling and condensing vapor in reflux condenser 103.The temperature of the wet liquid desiccant rises about another 5 C. toabout 20 C. in reflux condenser 103. The amount of temperature rise isprimarily dependent on flow rate of vapor through reflux condenser 103.Alternatively, tempered clean plant water can be used as the coolingfluid in both reboiler vapor condenser 120 and reflux condenser 103. Theliquid desiccant leaves reflux condenser 103 via line 122 and is thenheated to between about 100 C. and about 180 C. in heat exchanger 20.

The heated wet liquid desiccant leaves heat exchanger 20 and flows vialine 19 to flash drum 30 wherein substantially all dissolved lowmolecular weight vapors, including hydrocarbons and nitrogen, carbondioxide, hydrogen sulfide, are flash separated from the wet liquiddesiccant.

Flashed gas leaves flash drum 30 and flows via line 31 to cooler 32where hydrocarbons, water and any liquid desiccant present in the vaporstream are condensed. The cooled stream from cooler 32 flows throughline 33 to flash gas separator 34 wherein any noncondensed light endsare separated and vented from the system via line 35. This gas may beflared, utilized as a fuel source or otherwise recovered. The gas leavesthe system at an operating pressure of about 2.5 to about 6.0 Barg.

Liquid from flash gas separator 34, which contains hydrocarbons and wetliquid desiccant, leaves flash gas separator 34 via line 37 and joinsthe wet liquid desiccant flowing in line 39. The combined wet liquiddesiccant stream flows through line 41 to first stripping zone 40wherein the wet liquid desiccant is subjected to heating by reboiler 42and the stripping agent received from the overhead of second strippingzone 44 via line 46.

The combined wet liquid desiccant stream 41 is heated to about 150 C. toabout 205 C. in reboiler 42 wherein the liquid stream is partiallyvaporized, forming an equilibrium mixture of liquid and vapor. Theheating of the wet liquid desiccant and the action of the strippingsolvent remove from about 50% to about 95% of the water originallycontained in the combined wet liquid desiccant stream. Vapor from firststripping zone 40 which is at a temperature of about 85 C. to about 100C., is conveyed via line 45 to condenser 60, where it is partiallycondensed and cooled to a temperature of about 0 C. to 40 C. Fromcondenser 60 the cooled stream flows via line 61 to three-phaseseparator 62. The small amount of vapor that does not condense incondenser 60 may be routed from separator 62 via line 63 to a flare orother system that can accommodate this gas stream. The back pressure onthe solvent water separator will typically be in the range of about 0.05Barg to about 0.15 Barg, and may be as high as 0.35 Barg, permittingseveral routes for safe vapor disposal. Condensed water from separator62 is conveyed via line 65 to a condensed water pump 101 whichdischarges the condensed water into line 119, which in turn conveys thecondensed water to a conventional water treatment facility. Solventaccumulated in separator 62 exits via line 67 and is routed to pump 70.The solvent is discharged from pump 70 via line 71 and is directed vialine 74 to solid desiccant drying bed 75 of the solid desiccant dryerand if necessary, via line 72 as described below. The solid desiccantdryer is comprised of solid desiccant dryer bed 75 and solid desiccantbed 76. Solid desiccant drying bed 75 is depicted in drying mode andsolid desiccant bed 76 is depicted in regeneration mode. When soliddesiccant drying bed 76 is in drying mode, the solvent discharged frompump 70 via line 71 is directed to line 73 to solid desiccant drying bed76.

In solid desiccant dryer 75 the solvent is dried from an equilibriumwater content of about 100 ppm to about 2000 ppm (depending on solventcomposition and relevant water retention in hydrocarbon phase) down toabout 10 ppm to almost zero ppm. The dried solvent exits solventdesiccant drying bed 75 via line 77 and is then heated and vaporized inliquid desiccant cross exchanger 90. When solid desiccant drying bed 75is in regeneration mode, the dried solvent exits solid desiccant dryingbed 76 via line 78 and is then heated and vaporized in liquid desiccantcross exchanger 90. The vaporized solvent may be further superheated insuperheater 89 before entering the second stripping zone 44 via line 91.

A portion of superheated solvent vapor is diverted from line 91 to line92 and is used to dry the desiccant in solid desiccant drying bed 76,which is in regeneration mode. Moist superheated solvent vapor leavessolid desiccant dryer bed 76 via line 95 and is conveyed to line 45 vialine 98.

Once the moisture in solid desiccant bed 76 is removed by thesuperheated solvent, the flow of superheated solvent to solid desiccantdryer bed 76 is terminated and solid desiccant drying bed 76 is placedin cooling mode. A portion of dried gas is diverted from line 13 andconveyed via line 14 and then line 94 to solid desiccant dryer bed 76.Dry gas flows through solid desiccant dryer bed 76, cooling thedesiccant and then leaves solid desiccant dryer bed 76 via line 95 andis transported via line 97 to a gas flare for disposal. Once the coolingmode is completed for solid desiccant drying bed 76, it can then beplaced in drying mode. When solid desiccant drying bed 75 is inregeneration mode and solid desiccant drying bed 76 is in drying mode, aportion of dried gas is diverted from line 13 and conveyed via line 14and then to line 93 to solid desiccant drying bed 75. Dry gas in thisconfiguration flows through solid desiccant drying bed 75 and uponexiting the bed, flows through line 96 and is transported via line 97 toa gas flare for disposal. Solid desiccant dryer beds 75 and 76 alternatebetween drying, cooling mode and regeneration mode automatically, everyeight hours, or a longer cycle, as solvent drying conditions require.

As an alternate to the above solid bed solvent drying, the solvent mayhave the entrained water only removed by a solvent coalescer. The fullstream of 115 is introduced to solvent coalescer 116. The water isrecycled via stream 117 to vessel 62. Resultant solvent in stream 118continues and is heated by cross exchanger 90.

Hot, partially regenerated liquid desiccant flows from reboiler 42 vialine 43 to second stripping zone 44, a conventional stripping column. Insecond stripping zone 44, substantially all the remaining water in theliquid desiccant is removed by the stripping action of the strippingagent, dry vaporized solvent. The stripped water and stripping agentleave second stripping zone 44 via line 46 and are delivered to firststripping zone 40. Liquid desiccant that is substantially dry leavessecond stripping zone 44 from outlet 47 and flows to surge vessel 48.Dry liquid desiccant leaves surge vessel 48 via line 49 and suppliesheat for vaporizing the solvent in liquid desiccant cross exchanger 90.The partially cooled dry liquid desiccant leaving cross exchanger 90 istransported via line 21 to heat exchanger 20. In heat exchanger 20, thepartially cooled dry liquid desiccant is further cooled by indirect heatexchange with wet liquid desiccant. The partially cooled dry liquiddesiccant is then pumped by liquid desiccant pump 50 to heat exchanger51 for further cooling before entering contacting zone 10 via line 15 asdescribed above.

Internal reboiler vapor condenser 120 which is located in the vaporspace inside reboiler 42 condenses a portion of the equilibrium vaportherein, forming a reboiler vapor condensate which contains both waterand liquid desiccant. The reboiler vapor condensate collects in tray 104and is conveyed via line 106 to condensate accumulator vessel 105.Condensate in accumulator vessel 105 is pumped via condensate pump 113to line 114, wherein it combines with liquid from flash gas separator 34and wet liquid desiccant from flash drum 30. Alternatively, reboilervapor condensate from condensate accumulator vessel 105 is conveyed vialine 107 to surge vessel heat exchanger 108, wherein the reboiler vaporcondensate is heated by indirect contact with dry liquid desiccant. Theheated reboiler vapor condensate is then conveyed to a conventionalsteam trap 109 wherein water vapor is released via vapor line 110 andliquid desiccant is recovered via line 111 and sent to storage vessel112 for eventual reuse.

Solvent will be produced if the wet gas stream has adequate amounts ofsuitable components, such as light hydrocarbons, that are absorbed bythe liquid desiccant in contactor 10. This compensates for varioussolvent circulation losses. If excess solvent is thus produced, it isdiverted from the discharge of pump 70 through discharge line 72 tostorage or other uses. If the solvent obtained from the wet gas isinsufficient to compensate for various solvent circulation losses, freshsolvent is added to the system.

EXAMPLE 1

A wet liquid desiccant solution of aqueous triethylene glycol (TEG)containing approximately 3.5% water was fed at the rate of 5.2 m² /hr toa regeneration system as depicted by the apparatus in FIG. 1 including areboiler 42 placed between a first stripper 40 and a second stripper 44.The first stripper and the second stripper contained respectively 1.8 mand 3.0 m of 1-inch pall ring packing. The reboiler was operated at 204C., resulting in a continuous stream of semi-regenerated TEG being fedto the top of the second stripper at 204 C. and contacted with solventvapors. The solvent vapors were superheated to 227 C. to supply the heatfor vaporizing water from the TEG. The solvent flow rate, measured as aliquid after it is pumped by the solvent pump, was maintained atapproximately 0.15 liters per liter of TEG fed to the contactor. Thislow solvent rate results in substantial energy savings over priorembodiments.

The overhead vapor from the first stripper was cooled in a water cooledcondenser to 38 C. wherein substantially all water vapor and solventwere condensed. The condensed solvent was separated form the water,dried in the solid bed dryer, and reused. At steady state conditions,the recycled solvent contained less than 1 ppm, of water by weight, andthe dry liquid desiccant contained less than 10 ppm of water by weight.The regenerated liquid desiccant contained 99.999 wt % TEG. This purityof TEG is capable of reducing the moisture content of the gas exitingthe absorber to about 0.1 ppm.

EXAMPLE 2

Example 2 was performed under the same operating conditions as Example1, with the exception that the condensate from the first stripperoverhead were subcooled to 10 C. using a refrigerant at 5 C. At steadystate conditions, the solvent in the first stripper overhead contained92 ppm water by weight. The solvent dryer eliminated virtually all theremaining water in the solvent. The dry liquid desiccant produced bystripping with this solvent contained 12 ppm water by weight and99.999+wt % TEG. This dry liquid desiccant can be used to dry a wetindustrial gas to a dew point of -80 C. or lower.

EXAMPLE 3

Under the same operating conditions of Example 1, natural gasoline wasused as the solvent. The solvent flow rate was maintained at 0.1 literper liter of dry liquid desiccant. At the steady state conditions, thedry liquid desiccant contained 28 ppm of water by weight. The naturalgasoline used as solvent was debutanized natural gas condensate,consisting of hydrocarbons in the range of C₅ to C₁₂. The resultantdried liquid desiccant produced by stripping with dried natural gasolinesolvent, was 99.998+wt % TEG . The TEG produced under these conditionscontained 20 ppm water.

EXAMPLE 4

A wet liquid desiccant solution of aqueous diethylene glycol (DEG)containing 5% water was fed at the rate of 2 liters per hour to theapparatus as described in Example 1. The reboiler was operated at 175 C.and the circulation rate of solvent at 200 C. was maintained at 0.14liter per liter of wet liquid desiccant. The resulting partiallyregenerated liquid desiccant leaving the first stripper contained 250ppm of water by weight. After the partially regenerated liquid desiccantwas stripped with solvent dried in the solid bed dryer, the dry liquiddesiccant contained less than 50 ppm of water by weight. The resultantdry liquid desiccant contained 99.99+wt % DEG.

EXAMPLE 5

A dry liquid desiccant comprised of TEG obtained from the processdescribed in Example 1 was fed to a glycol contactor 10 as depicted inFIG. 1 at the rate of 5.2 m³ /hr. A wet natural gas saturated with waterat 4 C. and 93 to 124 Barg was fed to the bottom of the contactor at therate of 7.08×10⁶ standard cubic meters per day. The contactor was packedwith 20 feet of structured packing. The contactor diameter was 2.10meters.

The dry gas removed from the top of the contactor contained less than0.1 ppm by weight of water with an equivalent dew point of -85 C. at theoperating pressure. The wet liquid desiccant removed from the bottom ofthe contactor was heated to 150 C. before feeding the flash tank. Theflash tank pressure was controlled to 3.5 Barg. The flash gas from thetank was cooled to 25 C. in an air cooled exchanger. A sample of thecondensate from the exchanger was collected in a solvent-water separatorover a period of twenty-four hours. The condensate thus recoveredcontained hydrocarbons in the C₃ to C₁₃ range, suitable for use assolvent in the liquid desiccant regeneration.

I claim the following:
 1. A method of drying a wet gas with a liquiddesiccant which comprises:contacting said wet gas with a substantiallydry liquid desiccant in a contacting zone to remove water from said wetgas and form a wet liquid desiccant and a dry gas product; heating andflashing said wet liquid desiccant to form a flash gas and a flashed wetliquid desiccant; passing said flashed wet liquid desiccant sequentiallythrough a first stripping zone and a second stripping zone; passing avaporized dry stripping agent sequentially through said second strippingzone and said first stripping zone in counter-current relation with saidflashed wet liquid desiccant to strip water from said flashed liquiddesiccant and form an overhead stream from said first stripping zone andsaid substantially dry liquid desiccant from said second stripping zone;maintaining said first and second stripping zones at temperaturessufficient to vaporize water but not decompose said flashed wet liquiddesiccant; heating at least a portion of said flashed wet liquiddesiccant found in said first stripping zone in a reboiler to form areboiler vapor; condensing at least a portion of said reboiler vapor toform a condensed reboiler vapor; removing said condensed reboiler vaporfrom said reboiler; cooling said overhead stream sufficiently tocondense water and stripping agent; separating resulting condensedstripping agent from resulting condensed water; contacting saidseparated condensed stripping agent with a solid desiccant to dry saidseparated condensed stripping agent and from said dry stripping agent;heating said dry stripping agent sufficiently to vaporize said drystripping agent; recycling said vaporized dry stripping agent to saidsecond stripping zone; and recycling said substantially dry liquiddesiccant from said second stripping zone to contact said wet gas insaid contacting zone.
 2. The method of claim 1, in which the liquiddesiccant is a glycol from the group consisting of triethylene glycol,diethylene glycol and monoethylene glycol.
 3. The method of claim 1, inwhich the wet gas comprises a gas from the group consisting of naturalgas, oil production facility gas, refinery gas, carbon dioxide,synthesis gas and hydrogen.
 4. The method of claim 1, wherein the liquiddesiccant is a glycol of 2 to 12 carbon atoms.
 5. The method of claim 1,wherein the stripping agent is naphtha.
 6. The method of claim 1,wherein the stripping agent is natural gasoline.
 7. The method of claim1, wherein the stripping agent comprises aliphatic hydrocarbons having aboiling range between about 40 C. and about 160 C.
 8. The method ofclaim 1, wherein the stripping agent comprises aromatic hydrocarbonshaving a boiling range between about 40 C. and about 60 C.
 9. The methodof claim 1, wherein the condensed reboiler vapor is returned to saidfirst stripping zone.